1. Field of the Invention
The present invention relates to a material that is in the form of hybrid crystalline three-dimensional lattices, in particular based on titanium, to the process of preparing same and also to the use thereof, especially for the storage of gases such as H2, CO2 or CH4, the adsorption of liquids, the separation of liquids or gases, applications in optics or in catalysis, in the biomedical field (controlled release of medicaments), cosmetic field, etc.
2. Description of Related Art
Metallo-organic lattices or metal-organic frameworks (MOFs) are coordination polymers, having an inorganic-organic hybrid framework that comprise metal ions and organic ligands coordinated to the metal ions. These materials are organized into one-, two- or three-dimensional lattices, in which the metallic species are joined together periodically by spacer ligands. The framework of these solids has both inorganic parts and organic parts, the cavities of which may be occupied by water molecules or by organic molecules that are easy to extract without deterioration of the backbone. This nevertheless results in a thermal stability lower than that of conventional inorganic porous solids (typically 300° C.); in compensation, the density of the hybrid phases is greatly reduced, typically between 0.2 and 1 g·cm−3, with, as a result, (BET) specific surface areas of up to 4500 m2·g−1, and pore volumes (<2 cm−3·g−1) that are considerably increased.
Another distinctive feature of certain hybrid solids is the existence of a flexibility of the lattice, greater than that encountered for purely inorganic phases. This is generally due to the use of flexible organic ligands (aliphatic chains), or to the shrinkage of the pores linked to the departure of molecules encapsulated within the pores.
These materials have a crystalline structure, are usually porous and offer many potential industrial applications such as gas storage, adsorption of liquids, separation of liquids or gases, catalysis, controlled release of medicaments, etc. Mention may be made, for example, of U.S. Pat. No. 7,279,517 which describes a reaction process involving a catalysis system comprising a zinc-based MOF material. This same material is also used for gas storage in U.S. Pat. No. 6,929,679.
Although MOFs exist with almost all the elements of the Periodic Table, from alkaline-earth elements (Ca, Mg) to transition metals (Sc, Fe, V, Cr, Co, Ni, Zn), 3p elements (Al, Ga, In) to rare earths (La, Ce, Eu . . . Y) and actinides (U), the number of porous MOFs based on titanium is still very limited.
Among all of the titanium-based MOFs synthesized to date, mention may especially be made of several types of open-framework titanium diphosphonates.
Among such disphosphonates, only an MOF of titanium obtained hydrotherrnally from TiO2 and from di-N,N′-piperazinebismethylenephosphinic acid (MIL-91(Ti): Serre C. et al., Chem. Mater., 2006, 18, 1451-1457) has a nitrogen-accessible porosity with a (BET) specific surface area close to 300 m2·g−1 and a pore size of the order of 4 Å. MOFs based on 1,4-butanediol or on phthalocyanine have also been identified recently without the latter having a significant specific surface area or porosity.
Although the first zirconium (IV) polycarboxylates were described recently, in particular in the article by J. Hafizovic Cavka et al., J.A.C.S., 2008, 130, 13850-13851, there is not, to date, any crystallized titanium (IV) polycarboxylate described in the literature.
International application WO2007/118888 refers to the synthesis of carboxylate MOFs based on titanium or on zirconium via a solvothermal route using a precursor of titanium such as, for example, TiOSO4, H2O and terephthalic acid in pure DMF, at a temperature of 130° C. for 18 hours. This process does not however make it possible to attain titanium-based polycarboxylate MOFs having a crystalline structure and a porosity that are satisfactory.